CRI and color temperature question

thebarefooter

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Hello. I am trying to find an explanation on the relationship between light color and CRI or more simply how lights can have the same color but different CRI's. For example how can a Malkoff m61n have a color of 4000k and a CRI of 95 but the neutral wildcat at 4000k has a CRI of 90, and the neutral hound dog in 4000k has a CRI of 80. I've tried to find an explanation online but have been unable to. Can anyone share another thread where I'm sure this has been discussed to help explain?
 

LEDphile

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CRI and CCT (color temperature) are independent measurements, although CRI is only meaningful if the light color is close enough to some shade of "white" that the color also has a CCT defined.

CCT describes a specific (range for the) color point. CRI describes how closely the light renders colors relative to a specific reference source (typically, a blackbody radiator for low CCTs and daylight for high CCTs).

In practice, CCT describes the color, and CRI describes the specific spectrum used to create that color - note that you can generate light with a CCT of 3000K in many ways, from mixing red, green, and blue monochromatic sources (CRI in the 30s), to heating a block of tungsten to 3000 Kelvin (CRI right around 100), to combining one or more phosphor colors with a blue LED (CRI options from around 65 up through over 95). This also means that two sources with the same color (same CCT and tint) but different CRIs will look the same on a white wall but look different when illuminating colored objects.
 

bykfixer

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CRI is an indicator of how acurate the color of an object appears to a computer when a light shines on it. Some say "as we see it".

With LED's there is a mixture of things to create a given tint appearance. But that "recipe" mixture that produces a given tint can create the appearance of more acurate color rendering or not. So there could be several "recipe's" that produce the same tint appearance but place more bias towards what the computer says is acurate or is not acurate by adding extra red or green etc while still appearing pretty close in tint to what those other recipes produce.

Example a light with a 4000 kelvin tint and CRI of 80 shone on say, a brown trash can may cause the "shade" of brown to appear somewhat lighter or darker or even make it appear more gray than brown. Where a light with the same tint but CRI of 95 would in theory cause the trash can to appear more closely acurate as compared to what you see in daylight.

The bias is subtle. It may cast a wee bit more orange than the others that also fit into the 4000k space, or more pink but still be deemed 4000kelvin. Example I know of is a 4500k Nichia 219B adds more red where the 219C adds yellow. Both are deemed 4500k but when aimed side by side at a white object appear different, but when aimed at your dog out in the back yard at night appear pretty much the same. Start tweaking the recipe to achieve that and CRI acuracy can be increased somewhat.

That's the best way I know how to explain it without going into a bunch of inside baseball stuff that's over my head anyway.
 
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KITROBASKIN

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Sounds like you are asking why the different CRI ratings with the same color temperature?
Different LED´s have different phosphor coatings that get different scores for CRI. Note that CRI does not really give a comprehensive idea of how a light performs. One opinion.
 

thebarefooter

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Sounds like you are asking why the different CRI ratings with the same color temperature?
Different LED´s have different phosphor coatings that get different scores for CRI. Note that CRI does not really give a comprehensive idea of how a light performs. One opinion.
Yes, basically I was wondering how the same color of light source can relay different information/CRI numbers about the objects you are seeing with that light to your eyes.
 
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CRI has "meaning" at 3000K and below, sort of, maybe, maybe up to 3200K, and at 5000K and above. Below 5000K, CRI is purely reference to how some color samples "look" compared to how they would like if illuminated with a black body radiator, i.e. a hot filament bulb. Few have any experience at all of a hot filament bulb above 3000K for illumination, as that is the highest typical for halogen bulbs, though some automotive run hotter, but that is not general illumination. Over 5000K and it is some agreed upon version of sunlight so we have a reference, sort of.

Simplest analog to the CRI. Mix a 3000K and 5000K LED in the right mix, and you will perceive 4000K. Mix a 2700K LED and a 6000K LED in the right mix and you will also perceive 4000K. The spectrums of each 4000K equivalent will be different.

4000K is what your eyes perceive when the light is shined into them. CRI is what your eyes perceive when that same light is used to illuminate objects with light of equivalent CCT. An LED/OLED screen can produce almost any perceived color of light with RGB, but when you use that light to shine on things, it looks much different from a white light of the same CCT.
 

aznsx

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Here's 3 (of many) of the URLs I saved when I was reading up on this subject, and they were somewhat helpful to me along the road I've personally travelled attempting to understand a bit about this very complex subject, and its impact on my choice of flashlights for my particular applications. They may or not be of help to you. They're examples of how lighting industry professionals attempt to explain some of these things to those who are not (like me):



 
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